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Friday, July 31, 2009

I've just received word from home that my official SWL callsign has arrived in the post.

I am now officially known as EI1597 !!!

That is official recognition that I am a Short Wave Listener (SWL), although it does not give me any permission or entitlement to transmit - at least until I get licenced!

So hopefully, I will only be known as EI1597 until October. If I should pass the exam on October 6th, I would then get a full callsign. At least if the unthinkable should happen and I fail, I will still have a "callsign" as such. I can report DX spots to DX Summit as an SWL, and participate in many activities, but at the end of the day I want the licence. So this is very much a temporary identification!!!

Thursday, July 30, 2009

Apparently even expert ornithologists can sometimes have difficult telling the gender of a particular bird, especially if watching from a distance.

But there is an extraordinary method of keen observation which will soon resolve the issue, especially where a male and female bird of the same species are standing close together. Even the ordinary Joe Soap can have an educated guess based on observation.

Yes, even you can probably tell quite easily just by having a good look.

Give it a try. Have a look at the photo below. Can you guess which of these two seagulls is the female?

Wednesday, July 29, 2009

OK, we're trying to cover the basic components of radio circuits in order to get to grips with the heavier stuff to come - circuit diagrams etc.

I tried Wikipedia for a definition of a diode, but it was a bit long-winded. Because I'm new to this stuff, and because many of you will be too, I prefer straightforward descriptions to help us more easily understand what these wee things do.

After a very quick websearch, I found the following from this website:

Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called valves.

I have not had time to study today due to work but might get 10 minutes in at lunchtime.

In the meantime, here is a warning to any HAM operator or SWL thinking of getting a new TV.

Avoid Plasma TVs like the plague. I got one a couple of years back and it causes 9db of interference on my HF radios. It affects especially the higher bands - 160M, 80M, 40M and 20M, but can be heard on all bands, even on a vertical antenna.

Here is a YouTube video demonstrating the effects of Plasma TV interference on 80 metres:

Always buy LCD.

I had a HF rig in the car for a few weeks not long ago, and the noise level would rise enormously as I pulled into the driveway. Even though my antennas for the home-base rigs are outside, away from the TV, it still causes huge interference. On 40 metres the noise blanks out any weaker signals so only the loudest can be heard - very annoying. I am planning to replace the TV with an LCD version at some stage which will hopefully eliminate the problem.

n. An electric circuit element used to store charge temporarily, consisting in general of two metallic plates separated and insulated from each other by a dielectric.

And we read that the capacitor, just like the bin lorry, stores the charge "temporarily" before returning it to the circuit. So far, so good. Just like a squirrel hoards nuts, a capacitor hoards electrons.

Then it gets a tad deeper, with the introduction of electric fields. No, not a new farming method. More like something from Star Wars. Read this from allaboutcircuits.com: "Whenever an electric voltage exists between two separated conductors, an electric field is present within the space between those conductors".

I'm paraphrasing the rest now: Circuits can be thought of as "conductive paths" through which electrons can flow. However, in the case of fields, we're talking about "interactions that can be spread across empty space". Hmmm. Deep. A "field" is an "abstract concept" - it doesn't have mass, and it does not need to exist within matter at all. Toying with two magnets and observing how they either attract or repel each other is a good way to imagine such a "field". (Although that's a magnetic field, not entirely dissimilar to an electric field). Think of Star Wars and "the force" and moving objects around by invisible forces. Field strength is measured in volts/meter, according to the IRTS disk.

It is found that when a battery or any other voltage source is connected to the two plates as shown a current flows for a short time and one plate receives an excess of electrons, while the other has too few. In this way one plate, the one with the excess of electrons becomes negatively charged, while the other becomes positively charged. If the battery is removed the capacitor will retain its charge. However if a resistor is placed across the plates, a current will flow until the capacitor becomes discharged.

UNIT - THE FARAD:

The basic unit of capacitance is the Farad, named after Michael Faraday. Maybe to help us remember this, we could think that a capacitor can only hold charge "for a day" - Far-a-day?

A capacitor has a capacitance of one Farad when a potential difference of one volt will charge it with one coulomb of electricity (i.e. one Amp for one second). (A coulomb, by the way, is six million million million electrons. I learned that last week, and can't believe I actually remember it! PS: That's a lot of nuts to be hoarded by our squirrel !)

A capacitor with a capacitance of one Farad is too large for most electronics applications, and components with much smaller values of capacitance are normally used. Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

One more thing to look at is capacitor charging and discharging, but I won't go into that right now because I need to get all the above into my head, especially the units of measurement. For now, I will post this wee image and try to get it into my head along with all the other stuff.

Any questions or observations, just pop me an email or a comment. And remember, I'm not teaching this stuff, I'm learning it! Thanks.

I was one correct question away from passing section C, and about 5 or 6 questions away from passing section A.I found section A to be the hardest as its 35 questions covering quite a few topics.I'm gonna resit the exam in October, and I hope to pass this time around, fingers crossed.I had trouble with circuit diagrams. If I had known them I think I would have passed.I find it hard to work out formulas etc.

I have no help or anything as I'm in Kilkenny and there's no classes etc around here, so it's kinda tough.I wonder if I could get some help from you, I mean if you could share the stuff that you're studying with me and see how it goes?.

Look forward to hearing from you.

Regards, Michael.

I would start by saying fair play Michael, congrats for giving the test a go. Then I would add that you have ten weeks today to get your act together and fill in the knowledge blanks. I have never sit the exam and I have it all ahead of me so I'm not entirely sure if I can help you, but I will be keeping the blog up to date with everything I learn, so certainly keep checking every day.

I would advise you to download the QADV program (QADV link), a lot of which is similar and relevant to the Irish test. I have been told that answering these questions repeatedly will eventually put the right answer into your head.

Get a couple of books - from your local library or from a radio club (our club in Dundalk has lots of them and I have borrowed them) and start studying the things you are weakest on.

I've been told that repeatedly drawing the circuit diagrams helps to put them in your head.

On the subject of formulae, I was never any good at maths at school. A friend who passed the exam was even worse, so don't worry too much. Is there anyone who can help you with these - perhaps a friend who is good at maths, a teacher, or another ham operator?

I have to say I admire you for taking the exam and for having the guts to sit it again. If you can get this far without help or classes, you are doing very well. Fortunately for me I will have the help of two licencees, but will still have to do a lot of the work on my own.

The most important thing for you to do now is study hard on the areas you are weak on. Start with section A. Look at the syllabus and the sample paper and then do the QADV questions. Split it into subjects. I studied "receivers" on its own for a few days and by the end of it I was getting 90% plus on the QADV test.

Hope I have been of some help and encouragement. See you on October 6th! (I hope!)

Monday, July 27, 2009

Apparently the easiest variable in any circuit to control is resistance, so probably the best place to start is with the humble resistor.

As the name would suggest, a resistor, erm, well . . . resists! Yes, it resists current and the lost current is dissipated as heat. Easy so far, right?

The most common schematic symbol for a resistor in a circuit diagram is a zig-zagged line. The resistors are labelled R1, R2, R3 etc, - resistor 1, resistor 2, resistor 3, blah blah and so on and so forth. They are also labelled with their resistance values, expressed in horse shoes. I mean Ohms. (Little joke! Ohm symbol is like an upside-down horse shoe). Anyway, moving swiftly on . . .

There are variable resistors also, just to make things complicated.

And because resistors dissipate heat they are rated according to how much energy they can dissipate without overheating and getting damaged. This is specified by the unit "watts". The power rating of a resistor is generally proportionate to its size, so the bigger the resistor, the higher its power dissipation rating. For more here is a great website - All About Circuits.

Update: Just did a 30-question test on receivers to refresh the memory. Got 29 out of 30 right, 97%. Buachaill Maith!

Right, now that I've been able to score 93% in the QADV test on receivers, I can move on a bit to something new. I thought that might be transmitters, but I have to leave that for a bit because I've been set a new task by Jedi Master Tony EI4DIB.

I'm going to do a bit of Googling on this one. Or perhaps a bit of Binging. You've heard of the new Microsoft search site, I presume? (Bing link)

I spent a bit of time on Friday learning about electrical pressure (volts), resistance (ohms), current and coulombs etc. Handy to know these basic things at the start.

But learning about the components themselves should act as a foundation for all the stuff to come, including circuit diagrams. I'll be honest, it all seems a bit daunting right now. Bloody heck, there's so much to learn. But I keep telling myself, if Brian EI7GVB did it in 8 weeks, I can do it in 10 !

I decided a couple of weeks ago that I was going to have a bash at the Amateur Radio exam, having been a Short Wave Listener for many years and a one-time 11-metre man with many QSLs from Europe.

The main motivation for this has been provided by my lifelong friend, Brian, who just last Friday received his callsign, EI7GVB, having successfully passed the test in June. Good man Brian. I look forward to working you on the bands!

I was completely daunted at first. Nay, overwhelmed. I looked at the QADV program and tried some questions and was absolutely bamboozled. I am not attending lessons with any radio club, nor engaging in private tuition. No, I'm going to do this myself, with a little help from my friends. Tony EI4DIB might just be one of those helpful friends!

In a matter of days, I have got my act together. I have learned Ohm's law, and the different variations. V = I x R, I = V/R, R = V/I. For resistors in series, add them up and apply the formula. For resistors in parallel, its R1xR2 over R1+R2. Easy peasy? Maybe not, but I think I have a grip on that. Next week it's capacitance and inductance.

Also I have launched into Module 4 of the IRTS Radio Experimenter's Exam Course Guide. Receivers. I'm trying NOT to think about the fact that there are 14 modules to be covered, but rather that I have over ten weeks left before I sit the exam.

Now I might have a wee bit of an aptitude for this stuff, but one cannot help feeling a little overwhelmed when one is starting down the road of learning a lot of stuff for an exam. However, I have applied myself well over the last few days to receivers, and was able this morning to draw a block diagram of a superheterodyne receiver from memory, including the BFO/CIO stage.

In addition, I tried three tests of 30 questions each last night using the QADV program (QADV link) on the subject of Receivers. I scored 90%, 90% and 93%, so something must be seeping through into that chasm in my head.

Some things might be worth mentioning here with are perhaps not explained in detail on the IRTS disk (Link to IRTS disk page). I have taken notes as I went along to help me fill in the knowledge gaps where the disk didn't seem to explain fully. Not that the disk isn't brilliant, just that I want to expand things a bit for anyone else who is studying for the exam.

Automatic Gain Control:

According to QADV, AGC is normally applied at the IF stages.AGC introduces distortion if applied at the IF stage. Why? Because the bias is too low.This distortion comes in the form of harmonics.The S-meter is usually driven from the AGC.What removes distortion caused by AGC to an IF stage of a receiver? The IF Transformers.AGC is usually obtained from the detector.